Theoretical study on the properties of TEMPO and its derivates losing an electron

A theoretical study on the properties of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and its derivates and each molecule losing an electron in vacuum and in acetonitrile were carried out using the density functional theory (DFT) at the (U)B3LYP/6-31g(d,p) level. The computational results show that different substituents obviously influence the second highest occupied molecular orbitals and the lowest unoccupied molecular orbitals, but the singly occupied molecular orbitals (SOMO) are similar and keep almost unchanged after each molecule losing an electron. Grouping the derivates by the linking atoms(O, N, C) of substituents shows the orderliness: in each group, with the reduction of electron withdrawing ability, the difference of the spin densities on O1 and N2 decreases, while the positive charge population of N2, the negative charge population of O1, bond length of O1—N2 and the energy of SOMO increase. After losing an electron O1—N2 shows obvious double bond properties and above half positive charge increases on O1 and N2. Through the analysis of the open-circuit voltage (VOC) of dye-sensitized solar cells using the derivates as redox mediator, it was found that the VOC were in linear correlation with SOMO levels and vertical ionization potentials.